A new design using a dielectric reflector to reduce the back radiation of aperture coupled antennas is proposed and developed in this paper. To validate the proposed design, a concise theory analysis is first conducted and then the proposed design is analyzed in a modified aperture coupled microstrip antenna. In this design, a radiating patch and a microstrip feed line are both etched on the same side of a top substrate and a coupled slot is etched on the opposite side of this substrate. To examine the effect of the dielectric reflector on the antenna performance, theoretical simulations and experimental investigations were carried out, and a good agreement between the theoretical expectation and the measured results validates the proposed design. The measured radiation patterns show that the proposed structure can offer a high radiation efficiency, a high front to back radiation ratio, and a high co-cross polarization ratio. With these features, the proposed design is significant in the electromagnetic interference and electromagnetic compatibility (EMI/EMC) designs for reduced undesirable radiation.